Before communicating with a terminal device, a base station first needs to perform uplink and downlink synchronization. During the downlink synchronization, the base station sends downlink synchronization signals by using a plurality of transmit beams. The terminal device receives and detects the downlink synchronization signals by using one or more receive beams, to obtain an optimal downlink transmit and receive beam pair, time information, and system information. The uplink synchronization is completed with help of a random access process. The terminal device first sends a random access signal. The base station detects the random access signal to obtain an optimal uplink transmit and receive beam pair, an uplink time, and the like, and to finally implement the uplink synchronization between the base station and the terminal device.
In a New Radio (NR) communications system, different random access resources may be in association relationships with different beams, or a base station uses different beams to receive uplink signals on different random access resources. Therefore, different beams of the base station may have different base station coverage areas. Terminal devices send uplink signals or receive downlink signals in different areas. The uplink signals received by the base station or the downlink signals received by the terminal devices have different demodulation or detection performance. As shown in FIG. 1, when a terminal device sends an uplink signal in a beam direction aligned with an area in which the terminal device is located, a signal received by the base station has best demodulation or detection performance; or when a terminal device sends an uplink signal in a beam direction non-aligned with an area in which the terminal device is located, a signal received by the base station has relatively poor demodulation or detection performance. Therefore, when implementing the uplink synchronization between the base station and the terminal device, the terminal device needs to select a suitable or an optimal base station receive beam to send an uplink signal or an optimal base station transmit beam receive a downlink signal in the random access process.
When the terminal device performs an initial access process, the terminal device first obtains beam information from a downlink synchronization signal block. Therefore, the downlink synchronization signal block should be in an association relationship with a random access resource. However, no solution for associating a downlink synchronization signal block with a random access resource is provided.